courier-imap: Remote Format String Vulnerability
— GLSA 200408-19

There is a format string vulnerability in non-standard configurations of
courier-imapd which may be exploited remotely. An attacker may be able to
execute arbitrary code as the user running courier-imapd (oftentimes root).

Affected Packages

Package

net-mail/courier-imap on all architectures

Affected versions

<= 3.0.2-r1

Unaffected versions

>= 3.0.5

Background

Courier-IMAP is an IMAP server which is part of the Courier mail
system. It provides access only to maildirs.

Description

There is a format string vulnerability in the auth_debug() function
which can be exploited remotely, potentially leading to arbitrary code
execution as the user running the IMAP daemon (oftentimes root). A
remote attacker may send username or password information containing
printf() format tokens (such as "%s"), which will crash the server or
cause it to execute arbitrary code.

This vulnerability can only be exploited if DEBUG_LOGIN is set to
something other than 0 in the imapd config file.

Impact

If DEBUG_LOGIN is enabled in the imapd configuration, a remote attacker
may execute arbitrary code as the root user.

Workaround

Set the DEBUG_LOGIN option in /etc/courier-imap/imapd to 0. (This is
the default value.)